"What standard" or "which standard"

[edmondjanet]

Teacher: What standard are you in?
Student: I am in standard 4th.
Today I taught this my students, but one of English teachers told me that, "Which standard are you in" is the correct. Totally, I am confused.
Which one is correct?
Thank you.

 

[bhaisahab]

Teacher: What standard are you in?
Student: I am in standard 4th.
Today I taught this my students, but one of English teachers told me that, "Which standard are you in" is the correct. Totally, I am confused.
Which one is correct?
Thank you.

Both are correct. I prefer "which" in this case.